Plasma has been frequently used in, for example, etching, deposition, oxidization and sputtering of a manufacturing process of semiconductor devices and flat panel displays (FPD) for an improved reaction of the treatment gas in a relatively low temperature. Conventionally, plasma has been generated using either a high frequency discharge of MHz range or a microwave discharge of GHz range for these types of plasma processing.
Plasma generated using the microwave discharge has an advantage in that high density plasma having low electron temperature can be generated under a relatively lower pressure, and in particular, large-diameter plasma can be efficiently generated by employing a slot antenna and a planar plate shaped microwave introduction window structure. It also has an advantage in that the plasma treatment device can be simplified since a magnetic field is not needed.
In particular, a radial line slot antenna among the slot antenna radiates microwave uniformly and widely from a slot plate having multiple slots arranged concentrically. As a result, a large-diameter plasma can be generated having an excellent uniformity of density and controllability can be generated.
In the meantime, the process being performed within a treatment vessel of the microwave plasma treatment device is occasionally controlled in real time through an in-situ monitoring. When an optical monitor device is installed on the microwave plasma treatment device equipped with such a slot antenna, it may be required to configure an optical waveguide for monitoring such that the optical waveguide does not affect not only the uniformity of electromagnetic wave radiation of the slot antenna, but also the uniformity of plasma density.
In regard to this matter, the optical monitor device installed in the plasma treatment device disclosed in Patent Document 1 uses a microwave transmission line which transmits microwave generated from a microwave generator toward a treatment vessel, in which the last section of the microwave transmission line is a coaxial line which is traverse from directly above at the center of the slot antenna in a vertical direction. The internal conductor of the coaxial line is configured as a hollow tube. The process performed within the treatment vessel is adapted to be optically monitored in-situ by making light pass through the hollow tube.
The optical monitor device is formed with a hole for the optical waveguide which penetrates through the center of the slot antenna to be continued with the hollow tube (internal conductor) of the coaxial line. In general, the center of the planar plate slot antenna is the center of a radial waveguide, and even if a through hole for the optical waveguide is formed at such a place, no influence will be exerted on uniformity of the electromagnetic wave radiation of the slot antenna, and thus no trouble will be caused in uniformity or controllability of plasma density.